Bummer, these really do seem to be the real weak link in the whole car: you often here stories of even quite fresh calipers giving trouble.
I can highly recommend Classicar (in the back of PorschePost): they did the TR ones: they arrived back on the day promised, as quoted, as new, and well packaged. Excellent all round. Obviously if you end up going this route you ought to get both done. At least they look pretty, so give a pychological improvement as well

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If you need their number give me a shout, and I'll dig it out.
DDK Member1243 07741 273865. Home of the RY Austin 7 Trophy's and Austin Single Seat Racers